In the automatic data identification industry, the use of RF transponders (also known as RF tags) has grown in prominence as a way to track data regarding an object on which an RF transponder is affixed. An RF transponder generally includes a semiconductor memory in which information may be stored. An RF interrogator containing a transmitter-receiver unit is used to query (or interrogate) an RF transponder that may be at a distance from the interrogator. The RF transponder detects the interrogating signal and transmits a response signal containing encoded data back to the interrogator. RF and RFID systems are used in applications such as inventory management, security access, personnel identification, factory automation, automotive toll debiting, and vehicle identification.
Such RFID systems can provide certain advantages over conventional optical indicia recognition systems (e.g., bar code symbols). For example, the RF transponders may have a memory capacity of several kilobytes or more, which is substantially greater than the maximum amount of data that may be contained in a conventional one-dimensional bar code symbol. The RF transponder memory may be re-written with new or additional data, which would not be possible with a printed bar code symbol. Moreover, RF transponders may be readable at a distance without requiring a direct line-of-sight view by the interrogator, unlike bar code symbols that must be within a direct line-of-sight and which may be entirely unreadable if the symbol is obscured or damaged. An additional advantage of RFID systems is that several RF transponders can be read by the interrogator at one time.
Existing RFID tags can operate in any one of several different frequency bands. Ultra High Frequency (UHF) tags operate around 900 MHz, high frequency tags operate around 13.56 MHz, and low frequency tags operate around 125/134 kHz. Depending on the application and environment, certain frequency bands may be preferred. It is generally accepted that no single frequency is the optimal frequency for all applications. To communicate with a given tag in the field, a tag reader must be able to communicate at a frequency shared with the tag.
Existing RFID tags can also operate according to any one of several different established protocols. Existing protocols can include EPC Class 0, EPC Class 1, EPC Gen 2, ISO/IEC 14443, and ISO/IEC 7816. These protocols are not necessarily interoperable. Thus, a reader capable of reading only one protocol may not be able to read a tag capable only of communicating using another protocol. To communicate with a given tag, a tag reader must be able to communicate using a protocol shared with the tag.